A survey of FLS2 genes from multiple citrus species identifies candidates for enhancing disease resistance to Xanthomonas citri ssp. citri.

Abstract

Pathogen-associated molecular patterns (PAMPs)-triggered immunity (PTI) is an important component of plant innate immunity. In a previous study, we showed that the PAMP flg22 from Xanthomonas citri ssp. citri (Xflg22), the causal agent of citrus canker, induced PTI in citrus, which correlated with the observed levels of canker resistance. Here, we identified and sequenced two bacterial flagellin/flg22 receptors (FLS2-1 and FLS2-2) from ‘Duncan’ grapefruit (Citrus paradisi, CpFLS2-1 and CpFLS2-2) and ‘Sun Chu Sha’ mandarin (C. reticulata, CrFLS2-1 and CrFLS2-2). We were able to isolate only one FLS2 from ‘Nagami’ kumquat (Fortunella margarita, FmFLS2-1) and gene flanking sequences suggest a rearrangement event that resulted in the deletion of FLS2-2 from the genome. Phylogenetic analysis, gene structure and presence of critical amino acid domains all indicate we identified the true FLS2 genes in citrus. FLS2-2 was more transcriptionally responsive to Xflg22 than FLS2-1, with induced expression levels higher in canker-resistant citrus than in susceptible ones. Interestingly, ‘Nagami’ kumquat showed the highest FLS2-1 steady-state expression levels, although it was not induced by Xflg22. We selected FmFLS2-1, CrFLS2-2 and CpFLS2-2 to further evaluate their capacity to enhance bacterial resistance using Agrobacterium-mediated transient expression assays. Both FmFLS2-1 and CrFLS2-2, the two proteins from canker-resistant species, conferred stronger Xflg22 responses and reduced canker symptoms in leaves of the susceptible grapefruit genotype. These two citrus genes will be useful resources to enhance PTI and achieve resistance against canker and possibly other bacterial pathogens in susceptible citrus types.

Endophyte Bacillus velezensis Isolated from Citrus spp. Controls Streptomycin-Resistant Xanthomonas citri subsp. citri That Causes Citrus Bacterial Canker

“…Citrus species are fruit crops that can be found worldwide, and they have high value in both fresh and processed fruit industries [1]. Because of the increasing demand for citrus fruits and juices, the global production of citrus fruit for 2018-2019 was forecast to expand from 4.2 million metric tons in the previous year to 51.8 million metric tons as favorable weather leads to larger crops in Brazil and the United States [2].…”

Response regulator VemR regulates the transcription of flagellar rod gene flgG by interacting with σ54 factor RpoN2 in Xanthomonas citri ssp. citri

“…In addition, the filament flagellin has been shown to be a pathogen‐associated molecular pattern, inducing innate immune responses in host plants (Zipfel et al ., ). Flagellin‐induced innate immunity plays a critical role in determining the resistance of citrus species to Xcc (Shi et al ., , ) .…”

Comparative transcriptome analysis during early fruit development between three seedy citrus genotypes and their seedless mutants

“…The cDNA synthesis was performed following the protocol as described. 36 RT-qPCR was performed using an ABI7500 thermal cycler (Thermo Fisher Scientific, Waltham, MA, USA) with Bright Green PCR Master Mix (Sigma-Aldrich, St Louis, MO, USA). Melting cures and electrophoresis were performed to verify the specificity and identify of the PCR products.…”